Online safety campaigners with opposing views have teamed up to urge Sir Keir Starmer to force social media platforms to prove they are safe before children can access them.
Ahead of the government's online safety consultation closing next week, six groups have written to the prime minister to press him to get platforms to earn the right to offer services to children.
They want social media platforms to meet strict safety standards before children can use them - and if they fail, then they should not be allowed to have young users.
The groups and charities are also calling for the PM to stick to his pledge of acting "within months" and not delay changing the law.
They have come together despite being on opposing sides of how to make it safer for children to be online.
Some have called for a social media ban for under 16s, while others warned that would push children into unregulated spaces.
But they have now said a binary debate between a ban or not can oversimplify a complex issue.
Their intervention is the first since Australia banned social media for under 16s, which has largely seen teens get around the ban.
Under the charities' proposal, children would have to be protected from harmful design as well as harmful content, with tech platforms not allowed to offer addictive design features to under 16s, including infinite scrolling, video autoplay, push notifications and streaks.
It would also ban features which present a risk to children's safety and wellbeing, such as disappearing messages, location sharing and the ability to be contacted by strangers.
The groups say legislation with their proposals would have to include a mechanism so they can be applied to any new features that put children at risk or exploit their attention.
The NSPCC, Smartphone Free Childhood, the Molly Rose Foundation, People vs Big Tech, FlippGen and the Future of Technology Institute have all signed the letter.
"This consultation is an opportunity to deliver the real change that children, parents, and British families across the UK are calling for," the letter says.
"We urge you to seize it - and to stick to your pledge to act 'within months not years'."
Andy Rose, chief executive of the Molly Rose Foundation, who had warned against an Australian-style ban, said: "Parents are rightly demanding action to protect children online and it's crucial the government acts quickly and decisively off the back of the consultation to make safety a precondition for tech firms to do business in the UK.
"There are united calls for safety by design to be embedded in online platforms used by children and the prime minister must use this impetus to commit to action.
"The time for tech exceptionalism is over and by standing with parents, children and civil society the Government can finally end the harm caused by big tech."
Joe Ryrie, co-founder of Smartphone Free Childhood, who has called for an under 16s ban, said: "Parents across the country are no longer willing to accept a system where tech giants are free to profit from children while families are left dealing with the harms their products cause.
"What's so significant about this moment is that organisations across civil society are aligning around a simple principle: access to our children should be treated as a privilege that must be earned, not an automatic right.
"The prime minister now has a historic opportunity not just to implement world-leading regulation, but to help reclaim childhood for a generation. He must seize it."
Laura Trott, shadow education secretary, said: "Children are being exposed to extreme and violent content on social media every single day. Boys are being fed material about knives and pornography, while girls are seeing content that makes them hate themselves.
"Until social media companies can prove their platforms are safe, they should not have access to our children. The Government have kicked this issue down the road, but I have continued to fight for stronger protections.
"We will keep holding Labour to account to make sure they deliver on their promise to introduce some form of age restrictions for under 16s, but they now need to get on with it."
A government spokesperson said: "We share the coalition's determination to keep children safe online and value the role they play in pushing for change. We want to give children the childhood they deserve and to prepare them for the future.
"That's why we launched a consultation examining everything from age restrictions to safer design features and addictive algorithms. We know families want us to move fast, and we've secured new powers to act quickly once the consultation concludes.
"This isn't a question of whether we will act, but how - we will set out next steps by the summer."
(c) Sky News 2026: Social media firms need to prove platforms are safe before children can use them, campaig
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